Beginning August, 1971, the clinical trial to evaluate the efficacy of total (simple) mastectomy with and without radiation and radical mastectomy was begun. At the present time, more than 800 patients have been admitted into the protocol from 32 institutions by more than 200 surgeons. Initially, patients are judged clinically to have negative or positive axillary nodes and randomized accordingly. The clinicaly axillary node patients are assigned to radical mastectomy, total (simple) mastectomy with postoperative radiation,, or total (simple) mastectomy alone. The clinically positive axillary node patients are assigned to radical mastectomy or total (simple) mastectomy with postoperative radiation. The study is increasing in tempo with approximately 50 patients per month being entered. It is premature to make statements relative to the efficacy of the various treatment modalities, however, interesting data has been obtained relative to auxillary material being collected. It has been demonstrated that patients randomized with the various treatment categories are similar according to a variety of criteria. Moreover, information has been accumulated relative to the pathology of the tumors. Information relative to complications of the various treatments has also been analyzed. The submission of data has been satisfactory. The delinquency rate for the entire study relative to forms not submitted is less than 6 percent. If patient accrual continues at the present rate for the next year, it should be adequate for the completion of the study.